The human papillomaviruses (HPVs) are associated with specific human cancers. Over 65 different HPVs have now been identified and over 20 of these are associated with genital tract lesions. The HPVs that are associated with genital tract lesions can be separated on the basis of their clinical associations into two distinct groups. One group, including HPV-6 and HPV-11, is generally associated with benign anogenital warts that infrequently progress to cancer and is considered "low risk." The "high risk" group, including HPV-16 and HPV-18, is associated with intraepithelial neoplastic lesions that are a comparatively high risk for malignant progression. It will be important to determine the role the HPVs play in the progression of a benign HPV associated lesion to a cancer. In HPV positive cancers, the viral genome is often integrated into the host genome. Integration occurs in a manner that preserves the integrity of the viral transcriptional regulatory region as well as the viral E6 and E7 genes which are invariably expressed in the cancers. The E6 and E7 genes of the high risk viruses encode oncoproteins which together can cooperate to efficiently immortalize primary human squamous epithelial cells, the normal host cell for the HPVs. The ability to immortalize primary keratinocytes is not a characteristic shared with the E6 and E7 genes of the low risk HPVs and it seems likely that this property may be linked to the oncogenic nature of the high risk HPVs. Insight into the mechanism by which these HPVs may be contributing to carcinogenic progression has come from the recognition that the oncoproteins encoded by these viruses and expressed in the cancers target and functionally inactivate key cell regulatory proteins, including the retinoblastoma and P53 tumor suppressor gene products. The E6 oncoprotein complexes with p53 and in doing so, stimulates its ubiquitination and proteolysis. The binding of E6 with p53 is mediated by an additional cell factor called E6-AP standing for E6-Associated Protein. The studies proposed in this application are designed to further characterize those features that distinguish the E6 proteins of the high risk and low risk HPVs, and to extend the studies on the structural and functional domains of E6-AP as they relate to E6 binding, p53 binding, and ubiquitination.